This invention relates to a continuous speed-shifting device in which a variable speed pulley mechanism and a differential gear mechanism are combined.
As an example of a belt type continuous speed-shifting device, there has been known the following device. This device is composed of a variable speed pulley mechanism which has variable speed pulleys and a V-belt wound between the variable speed pulleys. Each of the variable speed pulleys is composed of a fixed sheave axially non-slidably mounted on each of a pair of rotary shafts arranged in parallel with each other so as to rotate together with each of the rotary shafts, and a movable sheave axially slidably supported on each of the rotary shafts so as to rotate together with each of the rotary shafts. The fixed sheave and the movable sheave are opposed to each other so that a V-shaped belt groove is formed therebetween. The speed ratio between both rotary shafts is changed by varying an effective radius with respect to the V-belt by moving each movable sheave in its axial direction.
Meanwhile, there is proposed a continuous speed-shifting device in which the above-mentioned variable speed pulley mechanism and a planetary gear mechanism (differential gear mechanism) as a gear mechanism for speed shifting are combined, as disclosed in the Japanese Patent Application Laying Open Gazette No.62-118159.
In the above continuous speed-shifting device in which the variable speed pulley mechanism and the differential gear mechanism are combined, when an output shaft is made to rotate from its stopping state by using the differential gear mechanism, a power transmitting channel is divided into a driving power channel and a circulating power channel.
More specifically, in the closed-circuit type differential gearing, one of three gear elements of the differential gear mechanism is connected to the output shaft, and by varying the number of rotations of one of the remaining gear elements in such a manner as to regulate a speed ratio at the pulley mechanism, the rotating direction and the rotation speed are differentiated between the gear element and the remaining other gear elements, so that the rotating direction and the number of rotations of the gear element on the output side, namely, the output shaft, are determined. At this time, however, both the driving power and the circulating power are generated as motive power and output power is equal to the driving power minus the circulating power. Which of the two power transmission channels extending from an input shaft to the output shaft will become a driving power channel or a circulating power channel depends upon the number of rotations of the gear elements in the differential gear mechanism, and the gear element with the larger number of rotations becomes the driving power channel. The above number of rotations of the gear element means a circumferential speed on a pitch circle of the gear element.
In this case, in order to lessen the transmission load of the belt in the variable speed pulley mechanism, the output shaft is used in a state of rotating only in a set direction with respect to the rotation of the input shaft and at the time, the belt side of the variable speed pulley mechanism is made to be the circulating power channel on which circulating power smaller than driving power is transmitted.
When the above continuous speed-shifting device is applied for vehicles such as agricultural implements and other machines, however, since the output shaft rotates only in the set direction, there is required a normal and reverse rotation mechanism for switching the rotation of a driving wheel between normal and reverse directions in order to switch a vehicle running direction between forward and backward. This invites problems such as noise at the switching.
It is the primary object of the present invention to switch a vehicle running direction between forward and backward without providing a normal and reverse rotation mechanism individually when a continuous speed-shifting device in which a variable speed pulley mechanism and a differential gear mechanism are combined are mounted on a vehicle.
Another object of this invention is to accomplish compaction of a continuous speed-shifting device, simplification of its structure, reduce in the number of parts and cost reduction.
A further object of this invention is to simplify a structure of a torque cam mechanism.
A further object of this invention is to provide a continuous speed-shifting device having a structure so that variable speed pulleys and other elements can be maintained and inspected readily.